Concrete Durability Requirements in Public Works Projects

Concrete Durability Requirements in Public Works Projects

Speakers Ir. P. C. Wong Advisor of SCCT

Ir. Peter LEUNG Senior Engineer, CEDD

Content Part 1 Durability of Reinforced Concrete Structures

- Introduction - Factors Affecting Durability of RC

Structures - Deterioration of Structures - Measures to Improve Durability - Durability Tests

Content Part 2 Requirements for Durability in Public Works

Projects

- Cementitious Content

- W/C Ratio

- Workability

- Concrete Temperature Control

- Durability Requirements of Concrete

- Concrete Coating and Surface Treatment

Part 1

Introduction

Durability

Prof. A.M. Neville, “Properties of Concrete”

It is essential that concrete should withstand the conditions for which it has been designed, without deterioration, over a period of years. Such concrete is said to be durable.

Durability

BS8110 – Structural use of concrete

A durable concrete element is one that is designed and constructed to protect embedded metal from corrosion and to perform satisfactorily in the working environment for the life-time of the structure.

Durability

BS EN 1992-1-1:2004 Design of concrete structures. General rules and rule for buildings

• The choice of adequately durable concrete for corrosion protection of reinforcement and protection of concrete attack, requires consideration of the composition of concrete. This may result in a higher compressive strength of the concrete than is required for structural design.

• Strength = Durability ?

Design Life

Port Works Manual, 1996 edition

• The design life of a structure is taken to be its intended useful life, and will depend on the purpose for which it is required.

• Design life for all permanent marine structures should be 50 years.

Service Life

Structures Design Manual, HyD

• In the design of highway structures, due consideration should be given to durability during the service life. Achievement of durability is primarily affected by design and detailing, material specifications and quality of construction.

• The specific durability requirements of a structure should be assessed during the design stage and measures for their achievement should be considered.

Total Design Life Solution vs Maintenance & Repair Design Life Solution

• Commonly used 120 years design life

• Meaning of 120 years design life:

1. Total design life solution (i.e. no major maintenance) or

2. No replacement but continued maintenance

Factors Affecting Durability of RC Structures

External Factors

– Temperature

– Humidity

– Chloride

– Chemicals including sulphate

– Climate factors like sunshine, freeze and thaws

– Oxygen and bacteria

Summary of Hong Kong Climatic Data Over the Past 45 Years Description

Mean

Temperature

(°°°°C)

Range of

Mean Daily

Temp (°°°°C)

Mean

Relative

Humidity (%)

Jan

15.8

Feb

15.9

Mar

18.5

Apr

22.2

May

25.9

Jun

27.8

Jul

28.8

Aug

28.4

Sep

27.6

Oct

25.2

Nov

21.4

Dec

17.6

Annual

Mean

(mm)

23

3.7 3.2 3.0 3.1 3.1 2.7 3.3 3.2 3.4 3.7 4.0 4.0 3.4

71 78 81 83 83 83 82 81 78 73 69 68 77

Factors Affecting Durability of R.C. Structures

Internal Factors

– Quality of Raw Materials

– Mix Design

– Alkali Aggregate Reaction

– Workmanship

– Curing

Factors Affecting Durability of R.C. Structures

Other Factors

• Structural cracks and damages due to inadequate structural design and detailing, or concrete shrinkage

• Use of chemicals and seawater for household maintenance

• Concrete coating

Environments encountered

• Embedded belo w ground

• Submerged zone

• Tida l zone

• Splash zone

• Atmospheri c zone

Environments encountered

Deterioration of Structures




Deterioration due to AAR

Measures to Improve Durability

• Reinforcement

• Measures to Impair Corrosion Process

• Improvements on Concrete Properties


Reinforcement

• Galvanized stee l bars

• Epoxy coated reinforcement

• Stainles s stee l bars

• Carbon fibe r reinforcement


Reinforcement: Galvanized Steel Bars


Reinforcement: Epoxy Coated Reinforcement


Reinforcement: Stainless Steel Bars

Source: International Molybdenum Association


Reinforcement: Carbon Fiber Reinforcement


Measures to Impair Corrosion Process

Increase concrete cover

• Marine concrete (GS Section 21): Min. 75 mm



Coating – Silane protection

– Epoxy coating

Silane protection



Coal Tar Epoxy



Apply process such as impressed cathodic protection system

Corrosion Process

Anode: Fe --> Fe2+ + 2e

Cathode: 0.5O2 + H2O + 2e- --> 2OH

Durability Performance Tests

• Bulk Diffusion Test

• Chloride Ion Penetration Test


Bulk Diffusion Test


Bulk Diffusion Test


Bulk Diffusion Test

Ground powder

2.5

)ete 2

rcnoc yrd fo 1.5

ssam yb

%( 1

tnetnoC edi 0.5

rolhC

0

0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13 13-14

Distance from Core Surface (mm)

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Mix Without Micro-silica (Mix A)


Results of Bulk Diffusion Test

Mix With Micro-silica (Mix A/S)


CS1:2010 - Section 19 Determination of concrete’s ability to resist chloride ion penetration

Chloride Ion Penetration Test


Chloride Ion Penetration Test

Charge Passed Chloride Ion Penetrability (Coulombs)

>4000 High 2,000-4,000 Moderate 1,000-2,000 Low 100-1,000 Very Low

<100 Negligible

Part 2

Requirements for Durability in Public Works Projects

• Specification of concrete

Aim:

To achieve state of art concrete quality with good durability performance

Requirements for Concrete Durability in Public Works Projects

• Cementitious Content

• W/C Ratio

• Workability

• Concrete Temperature Control

• Durability Requirements of Concrete

• Concrete Coating and Surface Treatment

Cementitious content

Cementitious Materials

- Cement

- PFA or GGBS

- Microsilica

GS Section 16, (from Table 16.2 of GS):

Marine Concrete (GS Section 21)

– 380 kg/m3

Highways Project 1

– Grade 45: 350 kg/m3 for all pile caps and 400 kg/m3 for all bored piles

– Grade 60: 400 kg/m3 for deck span, crossbeams and towers

Highways Project 2– Same as GS

Drainage project– Same as GS

G rade strength (M Pa) 20 25 30 35 40 45 50

M inim um cem entitious

content (kg/m3)

270 290 310 330 350 375 400

Minimum Cementitious Content

Maximum Cementitious Content

GS Section 16- For water retaining/water tight structures: 400 kg/m3 if use PC;

450 kg/m3 if use PC and PFA- Other structures: 550 kg/m3

Marine Concrete (GS Section 21)- 450 kg/m3

Highways Project 1- Grade 45: 450 kg/m3 for all pile caps and 500 kg/m3 for all bored piles

- Grade 60: 550 kg/m3

Highways Project 2- Same as GS

Drainage Project- Same as GS

WSD Project- The total cementitious content for salt water water-retaining structure shall

not be less than 360kg/m3 and shall not exceed 430kg/m3.

Cementitious Content: PFA, GGBS and Microsilica

GS Section 16 Marine Concrete HyD project 1 HyD project 2 DSD project WSD Project(GS Section 21)

Requirements Optional use of Specified the use of Concrete grade 40 or Concrete grade 40 must Concrete grade 40 or PFA must be used.PFA & GGBS CSF with either PFA above must contain contain PFA. Grade 50 or above, PFA must be added.

or GGBS wither PFA or GGBS. 60 must contain CSF Grade 35 or below, eitherCSF may be used. PFA or GGBS shall be

added.PFA Normal concrete: 25 - 40% of total � 25 - 40% of the 25 - 40% of the specified 25-40% by mass of the 25-40% by mass of

not exceeding 35% cementitious specified minimum minimum cementitious cementitious content for the total cementitiouscontent cementitious content content concrete of Grade 40 and content

Pile cape/ � Min. 35% for above for normalsubstructure: at Grade 60 concrete applicationleast 25%

GGBS 35-75% for normal 60-75% of total � 60-80% of the Not specified � 60-75% by mass of Not specifiedconcrete cementitious specified minimum cementitious content for(Proposed) content cementitious content normal application

� Min. 60% for � 60-90% by mass ofGrade 60 concrete cementitious content for

low heat applicationMicrosilica Not specified 5-10% of total Up to 8% of the � Generally > 8% 5-10% by mass of the Not specified

cementitious specified minimum � cementitious contentMin. 8% by weightcontent cementitious content of cementitious material

for Grade 50 and 60concrete

Maximum water/cement ratio

GS Section Marine Concrete HyD HyD DSD WSD project16 (GS Section 21) project 1 project 2 project

Grade 60 0.35 0.35 -Grade 50 0.4 0.35 -

- Fresh water water-retainingGrade 45 0.4 0.38 -

structure: not exceed 0.55; notGrade 40 - 0.4 0.4

exceed 0.5 when PFA cementGrade 35 0.5 0.38 0.4 0.45 0.45

are usedGrade 30 0.47 0.47 0.47 - Salt water water-retainingGrade 25 0.5 0.5 0.5 structure: not exceed 0.4Grade 20 0.6 0.6 0.6and below

Workability

GS Section 16- Minimum design slump shall be 75 mm

Marine concrete (GS Section 21)- Same as GS Section 16

HyD project 1- Same as GS Section 16

HyD project 2- The workability of concrete is not specified but shall be proposed by the

Contractor. Concrete workability of less than 75mm slump will not normally be acceptable.

DSD project- Same as GS Section 16

WSD project- Same as GS Section 16

Concrete Temperature ControlHyD project 1

o– Concrete grade 40 and above: placing temperature shall not exceed 30 C; grade 20 –

40, not exceed 32oCo

– If section >= 500mm, placing temperature shall not exceed 25 Co

– Peak temperature shall not exceed 70 C; if contain at least 25% PFA or 45% GGBS, o

then the peak temperature shall not exceed 80 Co

– For large section, temperature differential (center to surface) shall not exceed 30 C. The max temperature difference between any points at 600mm apart shall not

oexceed 30 C.

HyD project 2o

– Placing temperature shall not exceed 32 Co

– Peak temperature shall not exceed 70 Co

– Temperature gradient (center to surface) shall not exceed 20 C per mDSD project

o– Concrete grade 45 or above, the peak temperature shall not exceed 70 C. The

omaximum temperature difference (center to surface) shall not be greater than 20 C per m

o– Concrete grade 40 or below, placing temperature shall not exceed 32 C

WSD projecto

– Placing temperature of concrete for water retaining structures shall not exceed 32 C

Durability Requirements of Concrete

GS Section 16 and Marine Concrete (GS Section 21)– None, except strength requirements

HyD project 1– Grade 60 concrete: AASHTO T277-93, Mean value less than

1000 coulombs at 28 days

HyD project 2– Same as GS Section 16

DSD project– Water sorptivity test: not exceeding 0.07 mm/min

– AASHTO T277 at 28 days not exceeding 1000 coulombs

CS1:2010 - Section 19 Determination of concrete’s ability to resist chloride ion penetration

Other Durability Requirements

Sulphate Soundness of Aggregates

• GS Section 16- Magnesium sulphate soundness weighted average loss

shall not exceed 6%

• Marine Concrete (GS Section 21)- Same as Section 16

• DSD project 1- Maximum sodium sulphate soundness (ASTM C88)

weighted average loss shall be 6%

• DSD project- Similar to DSD project 1

Other Durability Requirements

Alkali-silica Reaction (ASR)

• PAH: Chapter 5, Appendix 5.9– Additional requirements imposed referring to GEO Report No. 167

• GS Section 16– Inert to ASR unless a control framework installed

• GS Section 21– Same as Section 16

• HyD project 1– Similar to GS

• HyD project 2– Similar to GS and PAH

• DSD project– Similar to GS and PAH

Concrete Coating and Surface Treatment

• GS Section 16– No particular requirement

• GS Section 21 (marine concrete)– PS to Model Specification for Protective Coatings for

Concrete. Allowing the use of epoxy resin, acrylate, polyurethane resin and monomeric isobutyltriethoxysilanecoatings.

• HyD project 1– Silane protection

• HyD project 2– No particular requirement

• DSD project– No particular requirement

End of Presentation

Thank you!

Documents

Concrete Durability Requirements in Public Works Projects